3 Forty-five impressions were made with each of the following materials: Impregun F (polyether), Permlastic (polysulfide) and Hydrogun (irreversible hydrocolloid). The selected disinfectants were: 1% sodium hypochlorite (Milton) and 2% glutaraldehyde (Glutacid ). They were freshly prepared for each experiment. The experimental groups were divided according to the diagram: Impression materials 1% Sodium hypochlorite (n = 20) 2% Glutaraldehyde (n = 20) Control group (n = 5) 10 min 15 min 10 min 15 min Ten impressions from each group of materials were immersed in glutaraldehyde solution for 10 min, and 10 impressions of the same materials were immersed for 15 min. The same procedure was carried out with the sodium hypochlorite solution. Five (5) impressions of each material were used as control group, without being immersed in any disinfectant solution. The impression materials were dispensed and mixed according to the manufacturer s recommendations at room temperature (22 ± 1C). A gradual, constantly increasing pressure was applied to a perforated metal cast in order to expel excess material. Afterwards, a 1 kg weight was placed over the cast and the impressions were separated from the tray after 6 minutes. They were measured immediately after the impression procedure, to prevent any risk of distortion. Next, every impression was immersed in a disinfectant solution for 10 or 15 minutes, removed and rinsed under cold running water for 30 seconds and dried with compressed air. Immediately after drying, the original impressions were magnified 30 and the distances between the lines AB, CD, AC and BD as shown in Figure 1 were measured three times by two examiners, for each elastomeric material. Irreversible hydrocolloid impressions were measured twice, because this material is more susceptible to syneresis and drench (Bayindir et al. 2, 2002). Mitutoyo digital measurement microscope (TM500) sensitivity of 1.0 µm was used. The analysis of variance (ANOVA) model was used to test the null hypothesis that there was no difference between means for a particular impression material for disinfectants and the control, and the Tukey test was used to analyze dimensional changes of each impression material after immersion. All the hypotheses tested were conducted at a 95% level of confidence. RESULTS A total of 135 impressions were made and distributed between control and experimental groups. A graphic presentation of the data in Table 1 includes means and standard deviations. Standard deviations ranged from to for alginate impressions, to for polyether and to for polysulfide. The results of the measurements obtained are expressed in millimeters. TABLE 1 means and standard deviations in millimeters. Material/Condition Means/AB Means/CD Means/AC Means/BD Alginate/control 24,062 ± ,108 ± ,197 ± ,094 ± Alginate/Hypochlorite 10 min 24,008 ± ,077 ± ,208 ± ,108 ± Alginate/Hypochlorite 15 min 23,871 ± ,804 ± ,191 ± ,182 ± Alginate/Glutaraldehyde 10 min 23,945 ± ,935 ± ,165 ± ,079 ± Alginate/Glutaraldehyde 15 min 23,983 ± ,982 ± ,166 ± ,071 ± Polyether/Control 23,997 ± ,049 ± ,182 ± ,125 ± Polyether/Hypoclorite 10 min 24,061 ± ,079 ± ,204 ± ,139 ± Polyether/Hypochlorite 15 min 24,083 ± ,106 ± ,215 ± ,140 ± Polyether/Glutaraldehyde 10 min 24,081 ± ,079 ± ,207 ± ,123 ± Polyether/Glutaraldehyde 15 min 24,089 ± ,097 ± ,208 ± ,115 ± Polysulfide/Control 24,103 ± ,092 ± ,220 ± ,175 ± Polysulfide/Hypoclorite 10 min 23,974 ± ,998 ± ,174 ± ,141 ± Polysulfide/Hypoclorite 15 min 24,062 ± ,067 ± ,171 ± ,172 ± Polysulfide/Glutaraldehyde10 min 24,102 ± ,080 ± ,193 ± ,154 ± Polysulfide/Glutaraldehyde15 min 23,994 ± ,985 ± ,188 ± ,161 ± Revista Odonto Ciência Fac. Odonto/PUCRS, v. 21, n. 53, jul./set

4 The Tukey Test was used to analyze the results and showed no significant dimensional changes in polyether and polysulfide impressions in all periods of disinfection with glutaraldehyde and sodium hypochlorite (p = 0.05). Neither polyether nor polysulfide impressions showed any statistically significant differences from their control measurements after soaking in the two disinfectant solutions. The null hypothesis for theses experiments was that the mean distances measured in the control group were the same, irrespective of the impression being soaked in either one of the disinfectant solutions. However, after the alginate impressions were disinfected with sodium hypochlorite for 15 minutes a significant change was observed when compared with control group. A reduction in measurement represented alginate shrinkage. Macro and microscopic porosities were also found. The differences attained 0.3 mm ( m) mainly in the largest distances (AB and CD). DISCUSSION The effects of different disinfectant solutions and times on three impression materials have been evaluated. There have been disagreements regarding their dimensional stability after the process (Drenon et al. 7, 1989; Johnson et al. 9, 1998; Setcos et al. 20, 1985, Thouati et al. 22, 1996). According to the specifications provided by the Disease Control Centers, chemical disinfectants such as chlorine compounds, formaldehydes, glutaraldehydes, phenols, and iodophors have the potential to eliminate hepatitis, herpes, and AIDS viruses in 10 to 30 minutes (Matyas et al. 14, 1990). In this study, the choice was to evaluate polyether, polysulfide and irreversible hydrocolloid, because they are hygroscopic and thus less stable than polyvinyl siloxanes. Sodium hypochlorite and glutaraldehyde were chosen because these disinfectants are more widely used. There are also various types of test blocks used (with full arch casts, cavities for inlays). For this study, the American Dental Association Specification nº 19 was chosen for standardizing the disinfection and impression procedures, because it s usefulness in dentistry has been professionally recognized. Individual acrylic resin trays were not manufactured for the impressions because of the risk of water absorption and introduction of other variations. Stainless steel trays were used instead. For the same reason, the gypsum material was not poured. The problem of disinfecting dental impressions (Lepe et al. 12, 2002), particularly irreversible hydrocolloid and hydrophilic ones, such as polyethers is a major concern. Herrera et al. 7 (1986); Merchant et al. 15 (1984), Langerwalter et al. 11 (1990) and Matyas et al. 14 (1990) did not find dimensional change after the use of a 0.5% sodium hypochlorite solution for 30 minutes. In this study, the concentration of sodium hypochlorite was 2 times greater, which could explain the differences in the results. However, Minagi et al. 16 (1987) showed that immersion in 2% glutaraldehyde for 60 minutes for irreversible hydrocolloid impression materials did not jeopardize surface details. When it was immersed in 1% sodium hypochlorite for 15 minutes, however, it was possible to observe statistically significant differences, and macroscopic alterations, like little craters, which can affect the final results of dentures, because these surface imperfections would be transferred to the cast, and subsequently to the final restoration. Although this study showed no significant linear dimensional changes in polyether impressions for any disinfectants, other studies have shown that a 15-minute immersion of this material adversely affected the resultant casts. The same authors recommended that polyethers should not be immersed in disinfectant, because they may expand in periods exceeding 5 hours (Bergman et al. 2, 1980; Chong et al. 4, 1969; Dellinger et al. 6, 1990, Drenon; et al. 7, 1989; Johnson et al. 9, 1998, Setcos et al. 20, 1985, Owen et al. 17, 1993; Sawyer et al. 19, 1974). Disinfection of the polyether impressions using an alcoholic glutaraldehyde solution (2%) and sodium hypochlorite solution (1%), for periods of 10 and 15 minutes led to nonsignificant variations in all measured distances (AB, CD, AC, BD) without loss of accuracy or surface detail, a result consistent with previous studies. (Johnson et al. 9, 1998; Drenon et al. 7, 1989, Johnson et al. 10, 1998). The results obtained with polysulfide impression disinfections shows no difference in mean values after all times of disinfection with both disinfectant solutions. The results of this research are important to the dentist to select the appropriate disinfectant solution for specific clinical conditions such as fabrication of study models, removable partial dentures or fixed partial dentures. CONCLUSION Within the limits of this study it can be concluded that disinfect immersion practices 264 Revista Odonto Ciência Fac. Odonto/PUCRS, v. 21, n. 53, jul./set. 2006

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